Electric motors that drive heavy loads require start windings to temporarily supplement run windings when starting. The de-energizing of the start winding once the electric motor has started is controlled by a mechanical centrifugal switch located on the motor shaft, wherein the centrifugal switch opens when the shaft reaches normal operating speed. In a clothes dryer, for example, the mechanical centrifugal switch has two sets of contacts, S1 and S2, that activate when the electric motor reaches a predetermined speed. S1 opens to de-energize the start winding which is no longer needed, and S2 closes to activate a heater circuit. The heater circuit is also controlled by other devices electrically connected in series with it in order to control the temperature of the dryer, but S2 ensures that the heater does not energize when the electric motor is not spinning. Though simple and inexpensive, mechanical centrifugal switches suffer from several problems and limitations, including that they have make noise when they open and close and can be prone to manufacturing quality issues.
This background discussion is intended to provide information related to the present invention which is not necessarily prior art.